In known transfer stations, machine frames of the face conveyor and of the gate conveyor extending at right angles thereto are constructionally combined to form a box frame. The individual runs of the face conveyor and of the gate conveyor are then arranged so as to intersect alternately inside the box frame, with the upper or top run of the gate conveyor located between the upper or top run and the lower or bottom run of the face conveyor, in such a way that the material is discharged, optionally with the assistance of a fender, from the top run of the face conveyor through an opening in its floor or tray into the top run of the gate conveyor located directly below it. Any fines which are entrained by the scraper chain assembly of the face conveyor passing over the opening in its tray are conveyed on to the deflection and driving drum of the face conveyor and thence back into the bottom run thereof. From the bottom run of the face conveyor the fines are dumped via an opening in the tray of the bottom run into the closed bottom run of the gate conveyor so that they are conveyed upwardly to the top run of the gate conveyor and are carried off therein together with the remaining material.
To achieve uninterrupted transfer of material from the face conveyor into the gate conveyor at the box frame, the opening in the conveyor tray of the face conveyor in the base frame is extended as far as possible over the complete width of the tray and over a specific length and at least one lateral wall profile, which serves to guide the scraper-chain assembly in the top run of the face conveyor, is removed in the region of the opening in the tray (see U.S. Pat. No. 4,673,079). As the scraper-chain assemblies of the face and gate conveyor are tensioned in the top run during the normal conveying operation, they cannot collide in the region where they pass through the box frame even if the scraper-chain assembly of the face conveyor passes through the region of the opening in the tray without guidance on both sides. During the return of the face conveyor, for example for transportation of material or for cleaning purposes and the like, however, slack chain may form in the top run of the face conveyor inside the box frame so there is a risk that the scraper-chain assembly of the face conveyor not guided in the region of the opening in the tray will collide with the scraper-chain assembly of the gate conveyor located therebelow.
To overcome this problem, it is known with transfer stations having the box frame as mentioned to arrange narrow support elements in the form of rods in the region of the opening in the tray to guide and support the scraper-chain assembly of the face conveyor. These support elements bridge over the tray opening in the box frame and are equipped with horn-like guide elements for the scraper-chain assembly (see DE-PS 26 00 999). These support elements are arranged rigidly in the box frame and during the normal conveying operation, the support elements are subjected to not inconsiderable wear. The support elements also constrict the discharge cross section of the tray opening of the face conveyor located in the box frame and this can obstruct the transfer of material.
It is also known with transfer stations with box frames as mentioned to remove part of the conveyor tray of the face conveyor inside the box frame only over part of its width so that the scraper-chain assembly of the face conveyor also rests on the remaining part of the conveyor tray as it passes through the box frame (see U.S. Pat. No. 4,766,992). A relatively narrow tray opening is produced in this case and this also hinders the transfer of material.
It is an object of the invention to design an improved transfer station such that excessive wear of means for supporting the scraper-chain assembly as it passes over the tray opening is prevented, the opening in the tray of top run of the face conveyor is as large as possible for uninterrupted transfer of material and collisions of the scraper-chain assemblies of face conveyor and gate conveyor with the formation of slack chain, which can appear during the return of the face conveyor, are avoided.